Insight into the microstructural evolution of anthracite during carbonization-graphitization process from the perspective of materialization

Materialization of coal is one of effective and clean pathways for its utilization. The microstructures of coal-based carbon materials have an important influence on their functional applications. Herein, the microstructural evolution of anthracite in the temperature range of 1000–2800 ℃ was systematically investigated to provide a guidance for the microstructural regulation of coal-based carbon materials.The results indicate that the microstructure of anthracite undergoes an important change during carbonization-graphitization process. As the temperature increases, aromatic layers in anthracite gradually transform into disordered graphite microcrystals and further grow into ordered graphite microcrystals, and then ordered graphite microcrystals are laterally linked to form pseudo-graphite phase and eventually transformed into highly ordered graphite-like sheets. In particular, 2000–2200 ℃ is a critical temperature region for the qualitative change of ordered graphite crystallites to pseudo-graphite phase,in which the relevant structural parameters including stacking height, crystallite lateral size and graphitization degree show a rapid increase. Moreover, both aromaticity and graphitization degree have a linear positive correlation with carbonization-graphitization temperature in a specific temperature range.Besides, after initial carbonization, some defect structures in anthracite such as aliphatic carbon and oxygen-containing functional groups are released in the form of gaseous low-molecular volatiles along with an increased pore structure, and the intermediates derived from minerals could facilitate the conversion of sp^(3) amorphous carbon to sp^(2) graphitic carbon. This work provides a valuable reference for the rational design of microstructure of coal-based carbon materials.

Energy transfer,superior thermal stability and multi-color emitting properties of langbeinite-type solid-solution phosphor K_(2)Dy_(1.5-x)Eu_(x)Ta_(0.5)(PO_(4))_(3)

Langbeinite type compounds are a large kind of oxometallate with good flexibility structure.Herein,we synthesized a new langbeinite type compound K_(2)Dy_(1.5)Ta_(0.5)(PO_(4))_(3),in which the Dy^(3+)and Ta^(5+)were blended to occupy the same crystallographic sites.Simultaneously,solid solutions of K_(2)Dy_(1.5-x)Eu_(x)Ta_(0.5)(PO_(4))_(3)(x=0-1.5)were prepared and their photoluminescence properties were investigated.Due to energy transfer from Dy3+to Eu3+,both Dy3+and Eu3+characteristic emissions are observed under 393 nm light excitation.The emitting color of K_(2)Dy_(1.5-x)Eu_(x)Ta_(0.5)(PO_(4))_(3)turns from green through yellow to red by simply adjusting the Eu^(3+)concentration from 0 to 0.4.Moreover,K_(2)Dy_(1.48)Eu_(0.02)Ta_(0.5)(PO_(4))_(3)phosphor possesses excellent fluorescence thermal stability and exhibits zero thermal quenching at 150℃.These results manifest that K_(2)Dy_(1.5-x)Eu_(x)Ta_(0.5)(PO_(4))_(3)solutions are promising multi-color emitting phosphors candidate for near-UV LED.

Graphene-like h-BN supported polyhedral NiS_(2)/NiS nanocrystals with excellent photocatalytic performance for removing rhodamine B and Cr(Ⅵ)

Human health is deteriorating due to the effluent containing heavy metal ions and organic dyes.Hence,photoreduction of Cr(Ⅵ)to Cr(Ⅲ)and degradation of rhodamine B(RhB)using a novel photocatalyst is particularly important.In this work,h-BN/NiS_(2)/NiS composites were prepared via a simple solvothermal method and a double Z-scheme heterojunction was constructed for efficiently removing RhB and Cr(Ⅵ).The 7 wt-%h-BN/NiS_(2)/NiS composites were characterized via a larger specific surface area(15.12 m^(2)·g^(−1)),stronger light absorption capacity,excellent chemical stability,and high yield of electrons and holes.The experimental result indicated that the photoreduction efficiency of the 7 wt-%h-BN/NiS_(2)/NiS photocatalyst achieved 98.5%for Cr(Ⅵ)after 120 min,which was about 3 times higher than that of NiS_(2)/NiS(34%).However,the removal rate of RhB by the 7 wt-%h-BN/NiS_(2)/NiS photocatalyst reached 80%.This is due to the double Z-scheme heterojunction formed between NiS_(2)/NiS and h-BN,which improved the charge separation efficiency and transmission efficiency.Besides,the influence of diverse photogenerated electron and hole scavengers upon the photoreduction of Cr(Ⅵ)was studied,the results indicated that graphene-like h-BN promoted transportation of photoinduced charges on the surface of the h-BN/NiS_(2)/NiS photocatalyst via the interfacial effects.

单原子Zn与高曲率碳基底耦合作用提高电催化CO_(2)还原

单原子催化剂(SACs)由于其最大的原子经济性、独特的电子和几何结构,已成为各种重要电化学反应中最具竞争力的催化剂之一.然而,单原子催化剂的载体对其催化性能上的影响并没有得到足够的重视.本文合成制备了N掺杂的碳纳米洋葱基底负载单原子Zn催化剂,研究发现该催化剂在电催化CO_(2)还原得到CO方面显示了很好的选择性,在-0.47 V(vs.RHE)时,CO(FECO)的法拉第效率高达97%.而且该催化剂也显示了优良的稳定性,在电催化还原100 h后,仍然具有80%的活性,这是已有锌基催化剂报道中的最佳活性.通过系统结构表征、电化学测试以及密度泛函理论(DFT)计算研究发现,高曲率的碳纳米洋葱载体对单原子Zn催化剂的活性有重要的影响,相比于二维石墨烯材料,高曲率基底有效改变单原子催化剂表面电荷密度,从而在催化剂与电解液界面处聚集大量的阳离子,有效促进对CO_(2)还原关键反应中间体的吸附,提高CO生成的选择性.